The advent of two-way messaging presents a wide variety of new problems. To understand some of the problems, knowledge of two-way paging or messaging from a system level would be useful. In particular, a two-way paging or messaging system typically has an infrastructure system including a plurality of outbound transmitters coupled to a controller for encoding, batching and scheduling the transmission of messages to be sent over the air to a plurality of portable two-way subscriber units. The subscriber units, not considered part of the infrastructure, transmit inbound messages that are received by at least one of a plurality of base receivers which are also coupled to the controller. Thus, the controller further provides the function of correlating outbound messages from the outbound transmitters with the inbound messages from the subscriber units.
Users of two-way messaging devices are typically users of paging systems that already provide nationwide service. Thus, these users expect the new generation of pagers to behave at least as well as the one they left behind. Two-way pagers, unfortunately only provide true two-way messaging services where there is good inbound coverage. Unfortunately, rapidly building out the inbound portion of a two-way messaging system is expensive. Another problem is that getting seamless coverage is an arduous task that requires careful measurement. It implies a time-consuming iterative process of finding optimal sites for additional receivers. In certain areas, two-way services are started using powerful transmitters at sites optimized for one-way paging by installation of a co-located receiver at each site. Unfortunately these receivers may not have the same range as the transmitters. Zones with such partial inbound coverage in the present invention will be referred to as one-and-a-half way zones or areas. They are often referred to as `leopard` zones because of the spotted pattern on the inbound coverage maps. Two-way pagers are known to function unpredictably in leopard zones, if they function at all.
Yet another problem is the high initial cost and slow market penetration of two-way units. Early exploitation of expensive spectrum can be aided by initial introduction of one-way pagers on the two-way frequencies. As two-way paging becomes more widely accepted and better supported by a range of applications, most one-way users will migrate to two-way devices. However, there is no way to move the remaining one-way pagers from the valuable two-way channels and to move legacy users to a few dedicated frequencies.
It is desirable to have a two-way messaging device, pager, or subscriber unit be able to operate in an area where there are no base receivers or where coverage is only provided by a one-way outbound base transmitter (or otherwise known as a one-way zone.) It would also be desirable to have a two-way messaging device use its two-way function as much as possible in areas where there is spotty inbound coverage without significantly degrading the battery life and other functions of the two-way messaging device. With existing two-way paging systems, the two-way subscriber device does not simply disable it's two-way functionality when the device detects that it is in a one-way zone. In fact, current two-way devices will not receive any messages until the system knows where the device is located since it cannot register in a one-way zone. Currently, the two-way device might display a prompt directing the user to call the service provider to notify the system of their current location. This "phone-in" registration is undesirable and creates an unnecessary burden on the user. Thus, a need exists for a communication system that allows a selective call transceiver for operation in a two-way coverage zone to seamlessly operate as a one-way selective call receiver in a one-way coverage zone or in other types of coverage zones or areas.